Unsafe Cabin Pressure

[RandallR 444]

Aha - that makes sense! I always found the "double-dump" confusing. BTW, I don't know whether you saw my post to Alex, but his repair of the Malibu pressurization system worked!Now, as far as the Hawker is concerned, I can tell you that you are correct, the plane will pressurize irregardless of any setting of the Main Air Valves.

[Roger Mazengarb 0]

G'day Alejandro,Sorry to say please disregard my previous post. I've been delving into the book and I have been confusing the dump valve with the safety valve.The rocker switch controls the SAFETY valve. Also the landing gear squat switch controls the SAFETY valve. It doesn't matter what position the rocker switch is in on ground as the squat switch on the MLG will open the safety valve.In the air the rocker switch can be used to open the safety valve and depressurise the aircraft.The press. control knob on the main panel operates what I would call a spill valve (piper call it a dump valve). what this valve does is to spill the air supplied by the twin turbo compressors to ambient should the pilot not wish to be pressurised. It also closes the firewall shutoff valve. Cabin press will fall and ram air will then enter the cabin through a check valve which was previously held closed by cabin pressurisation. I guess all TRI would model is knob in = air available for pressurisationpull knob out = air not available for pressurisation. Hope I haven't confused the issue.Cheers,Roger @YSSY

[Roger Mazengarb 0]

G'day Radall,I'm very red faced mate. I,ve been looking at Malibu course notes from about 15 years ago. I should have read them first. *:-*See my apology to Alejandro. There is a knob in the Malibu that dumps the t/c supply air to ambient if the pilot wishes not to fly pressurised. It operates firewall shutoff valves and OPENS a dump valve to spill the turbocompressor output to ambient. Whilst flying unpressurised ram air from a NACA scoop is automatically vented into the cabin through a check valve ( which is normally held closed by cabin pressurisation load.)I've attached the Piper recommended procedures for operating the Malibu pressurisation system.Thanks for checking out the Hawker. I was beginning to get a bit worried as to whether it was just me. I find the Hawker pressurisation system to be facinating. Such a realistic model; pity they missed the simple logic of the main air bleed valves OPEN/CLOSE.Cheers,Roger @YSSY

[RandallR 444]

No problem - thanks for the info!

[Guest Fly II Pilot]

Randall and Roger,I've looked into the logic for the Main Air Valves and indeed they do absolutely nothing. It may be possible to add some functionality to them but that will have to wait a bit. I'm way too busy right now...Regards,Alex

[RandallR 444]

Alex,That pressure dial indication I listed as a possible error may be nothing more than a differential indication - also, considering Roger's documents on the system's operation, your switch and control initial positions are fine. Nice work!

[Guest Fly II Pilot]

Randall,Glad to hear that because I was trying to invert the initial position and it was giving me a hard time because it's not a standard switch.Do you use the Malibu's Configurable Failures by Harry Gentilozzi? If so, I may have to make changes to the AMP file. Are you aware of any other updates with which this fix might conflict?Take care,http://www.avsim.com/hangar/fly/dfdg/banneraa.jpg

[RandallR 444]

Alex,I haven't used Harry's Failures program, so I can't speak to that issue.I am a little concerned about Roger's comment on the "bypass" push-pull on the panel. He talks about it being operational when pushed in, but bypassed when pulled out. I've always understood it to be the opposite (from Fly! 2K days) - pressurization was activated or available when the knob was pulled out??Regardless, it worked for me that way - I'll play around with it some more.

[Roger Mazengarb 0]

G'day Randall,>I am a little concerned about Roger's comment on the "bypass">push-pull on the panel. He talks about it being operational>when pushed in, but bypassed when pulled out. I've always>understood it to be the opposite (from Fly! 2K days) ->pressurization was activated or available when the knob was>pulled out??What I said is correct, for once. :-lolknob in = dump valve (7) closed, firewall shutoff valve (8) open, = t/c air into cabin = pressurisation working.knob out = dump valve open, firewall shut valve closed = t/c air diverted (dumped, spilled, whatever) to ambient = no pressurisation.If you dump the pressurisation air, the sonic venturis acting as flow limiters, may have trouble retaining sufficient air for engine supercharging. To maintain cabin pressure you need at least 20 inches Hg on the MAP gauge.I guess that's why the knob is guarded in the IN position.This knob basically just allows you to fly unpressurised and get ram air for ventillation. I'm not a pilot but as I understand it I think the normal position for this switch would be the IN position and left in that position on shutdown. See attachment. I've found another diagram that will help explain. A picture's worth a thousand words. ( or ten thousand of mine. :-lol )If Alejandro has "fixed" the Malibu then that's fantastic. Will we be seeing the modification uploaded; just as the modified pnl and amp files would be great. Cheers,Roger @YSSY

[RandallR 444]

Roger,I have no doubt that what you say is correct - what's bothering me is that the Malibu pressurized with the knob pulled out. We may have another case where TRI never "connected" it, just like the situation with the Hawker valve switches.I'll run some more test flights over the next couple of days just to be certain that there are no switch concerns, but I can certainly verify Alex's fix works great! I can't believe that I'm getting no warning lights anymore! :-) He should probably just upload the files.

[Guest Fly II Pilot]

Randall,Check your e-mail, I just sent you an update...Regards,http://www.avsim.com/hangar/fly/dfdg/banneraa.jpg

[Roger Mazengarb 0]

G'day Randall,OK I'm with you now. You are talking about the sim. I've been talking about the real aircraft. :-)I don't get any warning lights at 10,000 ft.I fly the malibu with the rocker switch in the "depressurise" position and the system seems to work OK. Haven't checked out the differential but all cabin pressure gauges appear to work OK.With Alejandro's fix does the aircraft still pressurise with the Knob pulled out?Cheers,Roger @YSSY

[Guest Eagle]

OK, now it is my turn again.What I have gathered from all of the writings is that the Main Air Valves (upper panel) on the Hawker do not work.I ran two tests on the Hawker.The following settings were the same for both flights:Cabin Pressure Altitude - 10,000Cabin Pressure Rate - 1,500Altitude - 14,000With the first test the Dump Valve was open during taxi and takeoff. After takeoff I shut the Dump Valve. There were no warnings up to 14,000 ft. Shortly after reaching 14,000 ft. all cabin pressure was lost and a warning was received.For second test the Dump Valve was again open during taxi and takeoff. After takeoff I shut the Dump Valve and turned on the Main Air Valves (two clicks). No warnings up to 14,000 ft., but, again shortly after reaching cruise all cabin pressure was lost and a warning was received.Any suggestions on this one? Want me to run additional tests?

[Roger Mazengarb 0]

G'day Wayne,>What I have gathered from all of the writings is that the Main>Air Valves (upper panel) on the Hawker do not work.That's correct, the valves are open irrespective of the switch position.>Cabin Pressure Altitude - 10,000>Cabin Pressure Rate - 1,500>Altitude - 14,000Hey Wayne take it easy. Those figures are not realistic. :-)For passenger (and pilot :-) ) comfort and well being, cabin altitude should never be set higher than 8000 ft. Above this the effects of Hypoxia start to manifest over time.Maximum rate of change should only be 300-500 ft/min.You will notice another "missed" feature. There is no provision for setting a negative cabin altitude. e.g. -1000 ft. BUT this is really only necessary for ground pressurisation for maintenance purposes and this is a FLIGHT sim for piloting the aircraft, so I guess one can't really complain. >With the first test the Dump Valve was open during taxi and>takeoff. After takeoff I shut the Dump Valve. There were no>warnings up to 14,000 ft. Shortly after reaching 14,000 ft.>all cabin pressure was lost and a warning was received.>>For second test the Dump Valve was again open during taxi and>takeoff. After takeoff I shut the Dump Valve and turned on the>Main Air Valves (two clicks). No warnings up to 14,000 ft.,>but, again shortly after reaching cruise all cabin pressure>was lost and a warning was received.Wayne I tried this and got different results to you.set 10,000 ft cabin altitude.set 1500 ft per min rate of changeset dump valve CLOSED for taximain air valves "OFF"Then went flying. :-)As cabin altitude reaches 10,000 the following occurs.1. Cabin altimeter pointer ( with the open triangle at the tip)indicates 10,000 ft2. Cabin rate of climb pointer falls to zero ( 9 O'clock position)3. "Cabin altitude" illuminates on the annunciator panel4. "Master caution" lights flashI cancel the master warning lights and am now flying at 10,000 ft cabin altitude (with the warning light ON) and the pressurisation system working in isobaric mode maintaining 10,000 ft. ( cabin altitude still being indicated on the .ppeeeerffeeeecct!!!! :-jumpyTried your #1 scenario - with same reults as I've just outlined.Are you absolutely sure that you are losing cabin pressure?. If you are this should be indicated by your cabin altitude pointer increasing to read aircraft altitude.Cheers,Roger @YSSY

[Guest Eagle]

Good evening, Roger. Like you I just hit the red button and turn off the warning.Looking at the Cabin Pressure dial the needle with the red x-hatch is about number 4. The white needle is at 1 1/2. The white needle will drop to 0 and the warning light comes on. The red x-hatch needle stays put.Hope this makes sense. I can live with the problem, just thought if it could be corrected that would be great.